Skin Effect
Induced currents allow magnetic fields to penetrate conductors only to a depth of about 4-5 skin depths. The skin depth is approximated by the following formula:
where
- w is the angular frequency, which is equal to 2pf (f is the frequency at which source currents and voltages oscillate during the solution).
- s is the conductor's conductivity in Siemens/meter.
- mr is the conductor's relative permeability.
- m0 is the permeability of free space, which is equal to 4p10-7 H/m.
Currents are concentrated near the surface of the conductor, decaying rapidly past the skin depth. As the formula above indicates, the skin depth gets smaller as the frequency increases.
For the 3D Eddy Current A-F, the skin effect is turn on automatically; it does not have to be requested in the Excitations > Set Eddy Effects window. Note that the Eddy Effect setting is grayed out because it cannot be turned off:
It is important to note that, as shown in the above equation, the skin effect only develops in domains with s > 0; consequently, non-conductive domains are automatically unchecked.
Activating eddy effects also allows the capture of the proximity effect.